Digital assistants are increasing popular. In a desktop or tablet environment, a user frequently multi-tasks including searching files or information, managing files or folders, playing movies or songs, editing documents, adjusting system configurations, sending emails, etc. It is often cumbersome and inconvenient for the user to manually perform multiple tasks in parallel and to frequently switch between tasks. It is thus desirable for a digital assistant to have the ability to assist the user to perform some of the tasks in a multi-tasking environment based on a user's voice input.